1. Technical Field
The current invention relates to an electrical fuse blow apparatus and method in integrated circuits. In particular, this invention relates to an apparatus and method for serially blowing selected fuses, in which each successive fuse blowing circuit is activated by a signal generated by a preceding fuse blowing circuit.
2. Background Art
In integrated circuits, fuses are frequently used to configure operation of a device or to provide redundant functionality that can be selectively disabled when a problem arises. In modern devices, thousands of fuses can be included on any one chip. Sizing considerations make it desirable to maximize the density in which these fuses are implemented. Because of size limitations with other types of fuses, electrical fuses are commonly selected to implement this functionality.
In configuring a device, it is often desirable to blow hundreds or even thousands of the fuses in a blow operation. Maximum efficiency would be obtained if all the desired fuses were capable of being blown simultaneously. However, each electrical fuse requires a certain amount of current to successfully be blown. Consequently, several problems arise when the simultaneous blowing of many fuses is attempted. For example, a poorer quality of fuse blowing (i.e., some fuses don""t blow or only partially blow) may result. Additionally, the thickness and width of the wiring in the circuit may need to be increased to accommodate a higher current.
As a result, several solutions have been suggested to limit the number of fuses blown at once during a fuse blowing operation. In one example, the blow operation is implemented in successive blow steps. Prior to each blow step, blow data is pre-loaded designating a limited number of the desired fuses to be blown. A blow clock then activates each of the designated blow circuits for a sufficient amount of time to allow the fuses to blow. This process is repeated until all the desired fuses have been blown. However, this solution has several disadvantages. First, several pre-loadings may be required to blow a large number of fuses. Additionally, the system often requires software support for performing the pre-loadings. Still further, since the fuses may require varying times before blowing, the blow clock must activate the designated blow circuits for a sufficient time to ensure that all fuses are properly blown.
Another solution allows all of the blow data to be pre-loaded at once. Subsequently, a blow circuit or a group of blow circuits is sequentially selected using, for example, a shift resistor control. In this fashion, a blow pulse is sequentially generated for each blow circuit or group of blow circuits. The blow pulse causes any designated blow circuit that is currently selected to be activated and the fuse to blow. The next blow circuit or group of blow circuits is then selected, and the process is repeated until all blow circuits have been included. While only a single data pre-loading is required, this solution attempts to blow fuses that are not designated for blowing. Further, a long blow pulse remains necessary to accommodate all fuses. Both solutions discussed also require a separate testing operation for each of the desired fuses to determine if it was blown properly.
As a result, there exists a need for a self-timed and self-tested fuse blowing apparatus and method. In particular, there exists a need in which each fuse blowing circuit remains active for only the necessary time to blow the particular fuse. Further, there exists a need for a fuse blowing apparatus that requires a simplified test to determine whether the fuses were blown properly.
The current invention provides an apparatus and method for serially blowing fuses wherein each succeeding fuse blowing circuit is activated by a signal generated by a previous fuse blowing circuit.
A first aspect of the invention provides an apparatus for blowing fuses in an integrated circuit, comprising: a plurality of fuse blowing circuits coupled serially, wherein each succeeding fuse blowing circuit is activated by an activate signal generated by a previous fuse blowing circuit.
A second aspect of the invention provides an apparatus for blowing fuses, comprising: a plurality of fuse blowing circuits coupled serially, wherein each succeeding fuse blowing circuit is activated based on an activate signal from a previous fuse blowing circuit and enabled based on an enable signal.
A third aspect of the invention provides a method of blowing fuses in an integrated circuit, comprising: serially coupling a plurality of fuse blowing circuits; generating an activate signal using an active fuse blowing circuit; and activating each successive fuse blowing circuit based on the activate signal generated by a preceding fuse blowing circuit.
The illustrative aspects of the present invention are designed to solve the problems herein described and other problems not discussed, which are discoverable by a skilled artisan.